1. Field of the Invention
The present invention relates to an ADSL modem apparatus and a re-initialization method of an ADSL modem apparatus that initiates a data communication after setting an optimal parameter according to a line condition through an initialization procedure.
2. Description of Related Art
With the widespread use of the Internet, there is an increasing demand for a high-speed access line that can be used for a fixed connection. Optical fiber is becoming more popular in the backbone of communication industries, and gigabit class super high-speed lines are starting to be employed in the key components of the backbone. However, most of the subscriber lines that connect user's home and storage centers of the communication industries are copper wire cables that are constructed for telephones. Therefore, an introduction of the xDSL technology that enables a high-speed communication of several M bits/second with a copper wire cable has been considered.
An ADSL method is one aspect of the xDSL technology. The ADSL method uses a much higher carrier frequency range of more than 35 kHz compared to the range used for telephones (less than 4 kHz). Therefore, a high-speed data communication can be performed using a telephone line, without hindering telephone functions.
FIG. 6 is a schematic illustration of a system configuration of a subscriber side. The storage center of a communication industry (center side) transmits signals to line 1. User's home (remote side) splits received signals from line 1 at splitter 2, inputting voice range signals (less than 4 kHz) into a telephone (POTS: Plain Old Telephone Service) 3, and high range signals (more than 35 kHz) into ADSL communication apparatus 4. ADSL communication apparatus 4 includes ADSL modem 5 and controller 6. Controller 6 controls data transmission/reception with data communication apparatus 7 (e.g., personal computer) and performs an initialization control for ADSL modem 5.
FIGS. 7 and 8 illustrate initialization sequence that is performed at ADSL modem 5 based on the ITU-T recommended G.992.1. In the example of FIG. 7, the control is arranged to perform a handshake procedure based on the ITU-T recommended G.994.1, prior to performing an initialization sequence.
In an initialization sequence based on the ITU-T recommended G. 992.1, the center side transmits C-RATES1 and C-MSG1 to the remote side, while the remote side transmits R-RATES1 and R-MSG1 to the center side. The center side informs the remote side regarding a general transmission speed for the downlink and uplink and additive information. In response, the remote side informs the center side regarding the remote side's transmission speed and additive information.
Then, both center and remote sides transmit training signals, C-MEDLEY and R-MEDLEY respectively, so that both center and remote sides check the reception conditions and determine carriers for carrier-off and bit number used for each carrier.
Further, the remote side transmits R-RATES-RA and R-MSG-RA, while the center side transmits C-RATES-RA and C-MSG-RA, so that the remote side can notify the center side of the capacity information of the remote side and information corresponding to a reception status (e.g., S/N), and the center side can notify the remote side of detailed information based on the reception result of R-MEDLEY (e.g., uplink and downlink transmission speed) and capacity information.
Then, the remote side transmits R-RATES2 and R-MSG2 to the center side, while the center side transmits C-RATES2 and C-MSG2 to the remote side, so that the remote side can inform the center side regarding the information such as capacity and uplink/downlink transmission speed determined by the remote side, and the center side can declare that the communication will be performed using capacity information, uplink/downlink transmission speed, and additive information determined by the center side.
Lastly, the center side transmits the declared capacity information, uplink/downlink transmission speed, and additive information as C-B&G to the remote side. The remote side transmits the capacity information, uplink/downlink transmission speed, and additive information instructed by the center side as R-B&G to the center side.
Then, B&G setting a carrier number for carrier off, bit allocation for each carrier to be used, gain information for the carriers to be used is finally exchanged, to complete the initialization sequence. Upon normally completing the initialization sequence, the data communication begins (SHOWTIME).
After a transition is made to the data communication, both center and remote sides monitor communication errors caused by factors such as a communication line abnormality. If the center side or the remote side detects a communication error, the above-described initialization sequence is performed again (performing an initialization sequence hereafter will again be referred to as “re-initialization process”), and restarts the data communication by setting an optimal parameter for the line condition.
However, in conventional ADSL modems, when the center side or the remote side detects a communication error, both sides recognize the need for a re-initialization process with the detecting side discontinuing the data communication and the other side detecting the discontinued data communication. When both sides recognize the need for a re-initialization, the re-initialization process is performed. Accordingly, data communication is always need to be terminated for a re-initialization process, thus making it impossible to provide an effective re-initialization process.